1. Field of the Invention
The present invention relates to a package structure for photoelectronic devices and a method of fabricating the same, and more particularly to a packaging and a fabricating method for a light emitting diode (LED) utilizing a silicon substrate.
2. Description of the Related Art
Among varieties of photoelectronic devices, LEDs are anticipated as the optimum light sources of the future for their compact size, high illuminating efficiency and longevity. In addition, due to the development of liquid crystal displays (LCD) and full color displays, white LEDs are now applied in consumer electronics products such as cell phones and personal digital assistants (PDA) as well as the traditional applications such as indication lamps and billboard displays.
Presently, research and development of LEDs is focused on improving the light extraction efficiency and resolving the heat dissipation problem. For the light extraction efficiency, the epitaxy process, the chip process and the packaging process can all be improved to enhance LED performance. The heat dissipation problem will mainly be solved by improving the packaging process, as advances are made in both the package structure and the package material.
For example, the light extraction efficiency of the reflective cup packaging type, one of several packaging types for LEDs, can be enhanced by increasing the light reflection rate. Furthermore, suitably modified designs of the reflective cup can also improve the heat dissipation efficiency. U.S. Pat. No. 6,562,643 put forth such a modified design, and U.S. Pat. No. 6,268,660 and U.S. patent publication No. 2004/0218390 have the same objectives. Moreover, U.S. Pat. No. 6,531,328 discloses that a silicon substrate 80 substitutes for a package substrate. Several reflective cups 81 are formed on the silicon substrate 80 by MEMS (micro electromechanical system) processes, as shown in FIG. 1. An insulation layer 82 and a metal layer 83 sequentially enclose the silicon substrate 80, and electrodes 831 and 832 are formed adjacent to the metal layer 80. Attached to the interior of each reflective cup 81 is an LED die 84, wherein the LED die 84 is electrically connected to the corresponding reflective cup 81 by bonding wires. An epoxy resin 85 encapsulates and therefore protects the LED die 84 in the corresponding reflective cup 81. There are two partial-depth holes 86 on each side of each reflective cup 81. The purpose of the two partial-depth holes, however, is not mentioned in U.S. Pat. No. 6,531,328.
FIG. 2 is a flow chart of the manufacturing process of the device in FIG. 1. As shown in Step S91, the silicon substrate 80 is first provided for these steps. Subsequently, a plurality of reflective cavities is formed on the first surface of the silicon substrate 80 by wet etching, as shown in Step S92. Referring to Step S93, electrode guiding holes are formed on the second surface opposite to the first surface by dry etching. Insulation layers are deposited on the surfaces of the silicon substrate 80 by a thermal oxidation method or a thermal nitrogenization method, as shown in Step S94. The insulation layers can be made of SiO2 or Si3N4. Subsequently, conductive layers are deposited on the insulation layers by electroplating, as shown in Step S95. Finally, a reflective layer is formed on the reflective cavities, and the electrodes 831 and 832 are arranged on the opposite surface by laser treatment, as shown in Step S96.
The aforesaid structure of the LEDs on the silicon substrate has several shortcomings. First, the reflective layer and the electrodes are made of the same material. There is currently no metal simultaneously suitable for optimizing both reflectivity and solderability. Furthermore, due to the fact that various LEDs emit light with different wavelengths, and that reflective efficiency of the metal is directly related to the emitting wavelengths, the optimal material for the electrodes varies accordingly. Solder is preferable for the material of the electrodes, but is not a suitable material for reflecting visual light. Au, Ag, Pd and Pt are better reflective materials, but none of these is suitable as material of electrodes.
In addition, the formation of the lowermost guiding holes adapts the dry etching technique, wherein the etched pattern has less adaptability in subsequent processes. Moreover, the metal layer needs laser treatment to form reflective surfaces, resulting in higher manufacturing costs.
In an R.O.C. patent publication (publication No. 200834970), the Applicant solved most of the problems of the aforesaid prior art. However, the resistivity of the silicon substrate adapted in R.O.C. patent publication No. 200834970 is required to be over 800Ω·cm. Otherwise, the solder may flow from the electrodes to the lateral surface of the silicon substrate and cause a short circuit. The manufacturing cost of high resistivity silicon substrate, however, is much higher than that of the low resistivity silicon substrate and is therefore the main drawback of the R.O.C. patent publication.
Consequently, there is a need in the optoelectronic market for high power photoelectronic devices or LED technology that is reliable and exhibits a simple structure that solves the aforesaid problems.